The production of flexible intraocular implants, whether for the anterior chamber or for the posterior chamber of the eye, raises a certain number of problems in order to facilitate convenient positioning of the implant inside the eye by the surgeon.
The interest of these flexible implants which are, in known manner, made either of hydrogel or of silicone gel, is that the optic portion of the implant may be bent about an axis orthogonal to the optical axis at the moment of being inserted inside the eye. It will be readily understood that such bending makes it possible to reduce the "overall dimensions" of the intraocular implant and therefore to reduce the size of the incision which must be made for positioning the implant in the eye. Traditionally, the desirable size of the incision made is at present 4 mm. This size is connected with that of the incision which must be made when it is desired to extract the lens typically by phako-emulsification. It is therefore necessary that the geometrical characteristics of the implant be such that, after being bent into two about an axis orthogonal to the optical axis, the optic portion may effectively pass through this incision of 4 mm.
Three types of problem arise in the definition of the geometry of the optic portion of the implant:
firstly, it is necessary that the maximum thickness of the implant, i.e. along its optical axis, be not too great in order effectively to allow the optic portion to bend and said optic portion to be maintained in bent position, with the aid of the surgical instruments usually used for this operation; PA1 it is also necessary that all the widthwise dimensions of the implant be sufficient for the optic portion to conserve its shape despite the stresses which may be applied thereto, particularly by the haptic portion of the implant, when the implant is positioned in the eye; PA1 finally, it is very important, for the precision of the positioning of the implant in the eye and for the comfort of the surgeon who is carrying out this operation, that the force necessary for maintaining the optic portion of the implant in this bent position, be substantially constant for a series of implants, whatever the optical power of this implant. Conventionally, the power of the implants usually positioned ranges from 10 to 30 diopters and, more commonly still, from 15 to 25 diopters.
Nevertheless, as in any implant, the surface of the correcting portion must be sufficient to avoid the parasitic phenomena, particularly in the case of slight displacement of the implant in the eye.
It should be recalled that the optical power of the implant is defined by the radii of curvature of the anterior and posterior diopters of the implant. It will be understood that the values of these radii of curvature, which participate largely in the definition of the widthwise dimensions of the implant, are overall imposed by the optical power which it is desired to produce with the aid of the implant, it being understood that the ratio between the radii of curvature of the anterior and posterior diopters of the implant may be played on.